1. Technical Field
The present invention relates to a circuit and an oscillating apparatus. More particularly, the present invention relates to a circuit including therein a logic circuit and a current amplifying circuit that amplifies the current of the signal output from the logic circuit and feeds the current-amplified signal back to the logic circuit, and to an oscillating apparatus which uses the above-mentioned circuit as a frequency dividing circuit.
2. Related Art
In a conventional logic gate circuit constituting a logic circuit, transistors are provided as switches between a high power supply with a relatively high potential and a low power supply with a relatively low potential. Here, the transistors may be field effect transistors (FETs), MOSFETs, high electron mobility transistors (HEMTs) or the like. The logic gate circuit outputs a logic signal in accordance with an input signal, for example, by connecting one of the high and low power supplies to the output terminal of the logic gate circuit depending on whether the switches are turned on or off.
Here, a logic gate circuit including therein two or more input terminals is provided with two or more transistors the bases of which are connected to the input terminals. Depending on the type of the logic operation which is desired to be performed by the logic gate circuit, the transistors may be connected in series to each other between the high and low power supplies in such a manner that the emitter of one of the transistors is connected to the collector of the other of the transistors. Take an example of a NAND circuit with two input terminals. The NAND circuit outputs the logic value “0” to the output terminal when the two inputs both indicate the logic value “1”. Therefore, the NAND circuit may be configured according to one embodiment in such a manner that the two transistors are connected in series to each other between the high and low power supplies and the bases of the transistors are connected to the input terminals. In this NAND circuit, when the two inputs both indicate the logic value “1”, the two transistors are turned on so as to connect the low power supply to the output terminal. As a result, the NAND circuit outputs the logic value “0”.
Here, it is necessary to generate a voltage of, for example, 0.9V between the base and the emitter in order to cause the transistors to operate. This necessity limits the number of transistors which can be connected in series between the high and low power supplies. In view of this, it is desired to realize a high-speed logic circuit with it being possible to keep the number of transistors which can be connected in series between the high and low power supplies equal to or smaller than a predetermined number.